PD is a clinical process used to determine the distance between eye pupils, and it is crucial in the optical industry to prescribe vision glasses.
The PD measurement is used to position the optical correction in the lens directly in front of the pupil. So, two PD measurements are most useful. This ensures that an individual is viewing through the center of the lenses. If an individual is not looking through the center of lenses, the vision may be blurry or distorted. The corrective lenses cannot be manufactured without a PD value.
An accurate PD requirement is even more critical as there are many variable points of focus in multifocal lenses, such as bifocal or progressive lenses. When the PD measurements are accurate, the value helps adjust the various fields of view in a multifocal lens to the optimal position. For the quality and accuracy of any lenses, the PD value is vital. With a PD, one can purchase eyeglasses from any source and not just where the exam was performed.
Moreover, the PD can change during childhood and adolescence but will almost certainly remain the same once an individual reaches adulthood. The average adult's PD is between 54-74 mm, and kids are between 43-58 mm.